| 641. |
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| 642. |
- Shen, L. F., et al.
(författare)
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Stability and quality factor of a one-dimensional subwavelength cavity resonator containing a left-handed material
- 2004
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 69:11
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Tidskriftsartikel (refereegranskat)abstract
- The characteristics of a one-dimensional subwavelength cavity resonator (SWCR) formed by a left-handed material layer and a right-handed material layer are studied. Some previously published conclusions for some fundamental issues are discussed and rectified. Our analysis for the stability and the quality factor of the SWCR shows that the two materials should be mismatched in the impedance in order to obtain a useful SWCR. It is shown that the resonant frequency of the cavity is closely related to the total thickness of the cavity. The total thickness can still be far less than the resonant wavelength if the thickness ratio of the two layers is chosen appropriately. The compactness of the SWCR is restricted by its stability and quality factor.
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| 643. |
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| 644. |
- Shen, L. H., et al.
(författare)
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Biomass mixing in a fluidized bed biomass gasifier for hydrogen production
- 2007
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Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509. ; 62:1-2, s. 636-643
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Tidskriftsartikel (refereegranskat)abstract
- To investigate the biomass mixing in the bubbling fluidized bed gasifier, a digital image processing based technique is developed in the paper. Red wooden balls are used as tracer particles to study biomass mixing in a two-dimensional fluidized bed gasifier. The experimental results show a high degree of biomass mixing in the vertical direction in the bed, whereas horizontal mixing in the bottom zone is found to be relatively limited. Along the vertical direction of the bed, a more uniform distribution of biomass particles is found at a low superficial velocity than at a high superficial velocity. With respect to lateral mixing, the biomass concentration in the center increases with the superficial velocity, whereas it decreases in the wall region. The biomass concentration in the bottom region decreases with the superficial velocity, but increases in the upper region of the bed. (c) 2006 Elsevier Ltd. All rights reserved.
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| 645. |
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| 646. |
- Shen, L., et al.
(författare)
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Interplay between relaxational atomic fluctuations and charge density waves in La2-xSrxCuO4
- 2023
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Ingår i: Physical Review B. - 2469-9950. ; 108:20
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Tidskriftsartikel (refereegranskat)abstract
- In the cuprate superconductors, the spatial coherence of the charge density wave (CDW) state grows below a temperature TCDW, the origin of which is debated. Using x-ray photon correlation spectroscopy, we have studied the temporal atomic relaxation dynamics in La1.88Sr0.12CuO4 to shed light on this question. Cooling within an emergent structurally distorted phase, which favors the CDW modulation in symmetry and develops in two stages between 180 and 120 K, we observe a crossover from cooperativelike to incoherentlike relaxation dynamics at TCDW=75(10) K. We argue that, if the CDW is hosted by this distortion, the concomitant relaxational crossover and enhancement of CDW spatial coherence supports the interplay between relaxational atomic fluctuations and CDWs in materials of this class on quasistatic times cales.
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| 647. |
- Shen, L., et al.
(författare)
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Magnetic microphase inhomogeneity as a thermodynamic precursor of ground-state phase separation in weakly coupled spin-3/2 chains
- 2021
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Ingår i: Physical Review B. - 2469-9950. ; 103:13
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Tidskriftsartikel (refereegranskat)abstract
- γ-CoV2O6 is a quasi-one-dimensional spin-3/2 magnet that possesses two distinct magnetic orders at low temperatures with propagation vectors k1=(½,0,0) and k2=(¼ + δh, δk, - ¼ + δl), respectively. Here we use muon spin relaxation and rotation to reveal the thermodynamics of the magnetic phase separation in this compound. In the paramagnetic (PM) region, short-range correlated spin clusters emerge at Tm ≃ 29 K at the partial expense of the PM volume. Upon further cooling, we show that these emergent clusters become spatially coherent and account for the k2 phase below TN2 = 7.5 K, while the remaining PM spins are driven into the k1 state at TN1 = 6.6 K. These results stress magnetic microphase inhomogeneity as a thermodynamic precursor for the ground-state phase separation in weakly coupled spin-3/2 chains.
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| 648. |
- Shen, L., et al.
(författare)
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Magnetic phase diagram of the quantum spin chain compound SrCo2V2O8 : A single-crystal neutron diffraction study
- 2019
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 21:7
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Tidskriftsartikel (refereegranskat)abstract
- We explore magnetic order in the quantum spin chain compound SrCo2V2O8 up to 14.9 T and down to 50 mK, using single-crystal neutron diffraction. Upon cooling in zero-field, commensurate antiferromagnetic (C-AFM) order with modulation vector=(0, 0, 1) develops below T N≃5.0K. Applying an external magnetic field (H∥c axis) destabilizes this C-AFM order, leading to an order-disorder transition between T N and ∼1.5 K. Below 1.5 K, a commensurate to incommensurate (IC-AFM) transition occurs at 3.9 T, above which the magnetic reflections can be indexed by=(0, 0, 1 ±δl). The incommensurability δl scales monotonically with H until the IC-AFM order disappears around 7.0 T. Magnetic reflections modulated by emerge again at higher fields. While the characters of the C-AFM, IC-AFM and the emergent AFM order in SrCo2V2O8 appear to fit the descriptions of the Néel, longitudinal spin density wave and transverse AFM order observed in the related compound BaCo2V2O8, our results also reveal several unique signatures that are not present in the latter, highlighting the inadequacy of mean-field theory in addressing the complex magnetic order in systems of this class.
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| 649. |
- Shen, L., et al.
(författare)
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Prior Pacemaker Implantation and Clinical Outcomes in Patients With Heart Failure and Preserved Ejection Fraction
- 2019
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Ingår i: Jacc-Heart Failure. - : Elsevier BV. - 2213-1779. ; 7:5, s. 418-427
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES This study examined the relationship between prior pacemaker implantation and clinical outcomes in patients with heart failure with preserved ejection fraction (HFpEF). BACKGROUND Conventional right ventricular pacing causes electrical and mechanical left ventricular dyssynchrony and may worsen left ventricular systolic dysfunction and HF. Whether conventional pacing is also associated with worse outcomes in HFpEF is unknown. METHODS Patient data were pooled from the CHARM-Preserved (Candesartan in Heart failure: Assessment of Reduction in Mortality and morbidity), I-PRESERVE (Irbesartan in Heart Failure with Preserved Ejection Fraction), and TOPCAT (Treatment of Preserved Cardiac Function Heart Failure with an Aldosterone Antagonist trial) studies and were examined for the association between having a pacemaker and the risk of the primary composite of cardiovascular death or HF hospitalization, the individual components of the composite, the 2 main modes of cardiovascular death (i.e., sudden death and pump failure death), and all-cause death in unadjusted and adjusted analyses. RESULTS Of the 8,466 patients included, 682 patients (8%) had a pacemaker. Pacemaker patients were older and more often men and had lower body mass indexes, estimated glomerular filtration rates, and blood pressures but higher concentrations of N-terminal pro-B-type natriuretic peptide than those without a pacemaker. The rate of the primary composite outcome in pacemaker patients was almost twice that in patients without a pacemaker (13.6 vs. 7.6 per 100 patient-years of follow up, respectively), with a similar finding for HF hospitalizations (10.8 vs. 5.1 per 100 patient-years, respectively). This risk rate persisted after adjusting for other prognostic variables (hazard ratio [HR] for the composite outcome: 1.17; 95% confidence interval [CI]: 1.02 to 1.33; p = 0.026), driven mainly by HF hospitalization (HR: 1.37; 95% CI: 1.17 to 1.60; p < 0.001). The risk of death was not significantly higher in pacemaker patients in the adjusted analyses. CONCLUSIONS These findings raise the possibility that right ventricular pacing-induced left ventricular dyssynchrony may be detrimental in HFpEF patients. (C) 2019 by the American College of Cardiology Foundation.
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| 650. |
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